Semiconductor scaling has resulted in device with very small features and increased complexity. Many integrated circuits now have features, such as traces or trenches that are significantly less than a micron across. While the reduction in feature size has allowed higher device density, more complex circuits, lower operating power consumption and lower cost, the smaller geometries have also given rise to new problems, or have resurrected problems that were once solved for larger geometries.
Silicon oxide is used as an insulating layer in many such applications. For example, silicon oxide is frequently used as pre-metal dielectric (PMD) layer below the metallization layer and above the active device regions. Such a PMD layer is deposited over a gate line below the metal lines.
Silicon oxide is typically deposited by thermal oxidation or by using a chemical vapor deposition (CVD) process or plasma enhanced CVD process. In a CVD process, a silicon containing gas is made to react with an oxygen containing gas resulting in the formation of the silicon oxide. Reaction rates and therefore the rate of deposition of a CVD process can be controlled using a combination of the temperature, pressure, reactant gas flow rates, and plasma power. The CVD processes result in the formation of silicon oxide, which is heated to form a silicate glass layer. The reflow of the deposited silicon oxide results in smoothing of the deposited oxide.
Boron and phosphorus are introduced into the silicate glass layers to form a doped silicate glass (BPSG) to improve the reflow and gettering behavior of the BPSG films. However, manufacturing with BPSG still poses many issues depending on the desired application. One example of a manufacturing challenge is the excessive reflow of the BPSG films, for example, resulting in difficulty to form proper contacts between dense pitched gate lines. Another example is the ability to completely fill a narrow trench in a void-free manner while keeping the thermal budget of the trench-filling process at a minimum.